1. Field of the Invention
The present invention relates to an optical system of a magneto-optical disk apparatus which reads a signal from an optical magnetic disk using polarized light.
2. Description of the Prior Art
In optical systems that use magneto-optical disk devices, a signal is read by detecting a slight rotation in the direction of polarization as a change of optical intensity due to the magneto-optic Kerr effect when a laser beam is reflected from the disk surface. The laser beam which is used is a linearly polarized beam for which a change in the direction of polarization is easiest to detect.
On the other hand, since a general optical element such as a mirror or a half mirror has a phase difference which is generated between a P polarized component and a S polarized component, the optical element changes the polarized condition of laser light. If such an optical element is used for the optical system of the magneto-optical disk apparatus which detects slight rotation of a polarized surface, the polarized condition of reflected laser light changes and a wrong signal be read from a disk.
In order to prevent this error, a non-phase difference coating, which cuts down the phase difference between the incident light and the reflected light of a polarized light, is given to optical elements such as a mirror and/or a half mirror used in the optical system of a conventional magneto-optical disk apparatus.
However, the cost of a non-phase difference coating given to the optical element is high, since the number of layers of a coating is large.